This invention relates to a gas turbine engine and more specifically to a variable area exhaust nozzle system associated with a gas turbine engine.
Many present day military aircraft must have the capability of accomplishing a number of missions and therefore the power plant, typically a gas turbine engine, is required to exhibit high performance characteristics over the entire range of possible operating conditions. In some instances it has become a necessity for this type of engine to include a convergent/divergent exhaust nozzle having a variable area both at the throat (at the downstream end of the convergent nozzle) and at the nozzle exit (at the downstream end of the divergent nozzle).
Variable area nozzles are well known in the art. Some prior art nozzles have an area ratio which is fixed by making the convergent nozzle integral and not movable in relation to the divergent section. Another approach makes movement of the convergent nozzle entirely independent from movement of the divergent nozzle and further providing for separate actuation of each nozzle. The first approach proved to have limited flexibility in optimizing the nozzle area ratio schedule for initial cycle requirements and in accommodating changes in cycle and mission requirements. The latter approach presented penalties in the way of complexity, weight and cost due primarily to the presence of dual actuators.
In an attempt to provide a variable nozzle offering to improve characteristics over these prior art approaches, the structure shown in U.S. patent application Ser. No. 814,568, filed on July 11, 1977, in the name of Arthur McCardle, Jr., and assigned to the same assignee as is this present invention was originated. Generally, this structure presented a variable area nozzle in which the convergent flap and divergent flap were pivotally linked together. Additionally, a single actuator was provided for closing the nozzle under appropriate operating requirements by a cam/follower arrangement associated with the convergent flap. The actuator closed the convergent flap which, in turn, closed the divergent flap due to the pivotal connection between the divergent flap and the convergent flap. However, the actuator was not used to open either nozzle but rather the pressure of the gases flowing through the nozzle was relied upon to provide appropriate force to open the convergent nozzle and the attached divergent nozzle.
The device presented in the above mentioned reference has generally worked satisfactorily and has proved to be a significant advancement in the state of the art. However, under certain transient conditions such as rapid deceleration to an idle condition the nozzle is required to double its area in a very short time approximating 1.2 seconds. Under these circumstances it has been found that the pressure of the gases flowing through the nozzle is not sufficient to open the nozzle. Since underside hooks or rollers were provided to engage the convergent flap for preventing the cam from disengaging the cam follower, the connection between convergent flap and the rollers results in the convergent flap being rapidly pulled open by the actuator via the underside arrangement. This results in damage to the underside hooks since the forces encountered in this action are greater than those forces capable of being withstood by the underside hooks or rollers. The present invention addresses this problem associated with this prior art variable nozzle.
It is therefore an object of the present invention to provide a variable area exhaust nozzle which is suitable for multi-mission aircraft application.
It is another object of the present invention to provide an improved variable exhaust nozzle of the type described in the aforementioned patent application.
It is yet another object of the present invention to provide a variable area exhaust nozzle which provides means for rapidly opening the nozzle in the event the pressure of the gases flowing through the nozzle are insufficient to accomplish this objective in the required time.